(1) Field of the Invention
The present invention relates to a method of inserting a wire into a pipe, a method of lining inside walls of a pipe, and an apparatus for running a wire through a pipe. More particularly, the invention relates to a method of inserting a wire into a pipe, comprising the steps of feeding a coil spring wire into a pipe while rotating the wire in a first direction, and thereafter retracting the wire out of the pipe while rotating the wire in a second direction opposite to the first direction, a driving force resulting from the rotation of the coil spring wire being applied to the wire in directions of movement thereof at a position where the coil spring wire is caught by the pipe both when the wire is fed into the pipe and when the wire is retracted out of the pipe. The present invention relates also to a method of lining inside walls of a pipe, which utilizes the foregoing method, and to an apparatus for inserting a wire into a pipe, which is used for executing these methods.
(2) Description of the Prior Art
The known method noted above for inserting a wire into a pipe employs a wire in the form of a coil spring having a circular cross section as shown in FIG. 16.
When the coil spring wire 43 is advanced through the pipe or retracted from the pipe, an external force F resulting from the rotational resistance of lining bodies and the coil spring wire 43 rotates the wire 43 in an unwinding direction to increase the coil diameter of the wire 43 from D3 to D4 as illustrated. In order to overcome this situation, the wire diameter may be increased or the coil spring wire 43 may be formed of a strong material for increased wire strength. But then the wire 43 will become less flexible, which impairs wire feeding into the pipe because of the presence of bent pipe parts. Conversely, where the coil spring wire 43 has increased flexibility, the wire 43 will become crumpled into a zigzag shape due to the external force F, and unable to rotate due to frictional contacts with the pipe. This situation makes the wire running impossible, and tends to deform and/or break the coil spring wire 43. Thus, the known method has room for improvement.
Where the above known method is used for lining inside walls of a pipe, satisfactory results cannot be obtained because of the difficulties encountered in running the wire through the pipe as noted.
The known apparatus for inserting a wire into a pipe has the problem of developing zigzagging and kinks of the wire when advancing or retracting the wire, in addition to the drawback relating to the use of the coil spring wire as noted above. The known apparatus is vulnerable to trouble particularly when inserting a wire into a pipe including many bent positions.